Phosphatidylinositol 3 phosphate

Phosphatidylinositol 3-phosphate (PtdIns3P or PI3P) is a phospholipid found in cell membranes that helps to recruit a range of proteins, many of which are involved in protein trafficking, to the membranes. It is the product of both the class II and III phosphoinositide 3-kinases (PI 3-kinases) activity on phosphatidylinositol.

PtdIns3P is dephosphorylated by the myotubularin family of phosphatases, on the D3 position of the inositol ring, and can be converted to PtdIns(3,5)P₂ by the lipid kinase PIKfyve.

Both FYVE domains and PX domains – found in proteins such as SNX1, Hrs, and EEA1 – bind to PtdIns3P.

The majority of PtdIns3P appears to be constitutively synthesised by the class III PI 3-kinase, Vps34, at endocytic membranes. Class II PI 3-kinases also appear to synthesise PtdIns3P, their activity however appears to be regulated by a range of stimuli, including growth factors. This suggests that specific pools of PtdIns3P may be synthesised upon cell stimulation.